Among various high-molecular materials which are industrially useful, carbon materials are excellent generally in such characteristics as heat resistance, corrosion resistance and lubricating property. Further, since they can be imparted with a variety of functions by the adequate control of production conditions and additional treatment conditions, they are being used in various fields as fibers or moldings of desired shapes depending on the individual use purposes.
Of these carbon materials, fibrous materials are usually produced by heat-treating their precursor fibers to make them infusible, followed by carbonization and graphitization at higher temperatures. However, this process involves complex production steps and moreover requires carbonization and graphitization treatments at high temperatures, so that the resulting carbon materials are relatively expensive and therefore have had limited uses in spite their excellent characteristics. Hence, in the field where high strength or high-temperature heat resistance is not particularly demanded, it has been proposed to use fibrous carbon materials in the form of so-called flame resistant fibers which are not completely carbonized, formed by burning organic fibers at comparatively low temperature.
Further, it has been attempted to introduce sulfo groups into organic high-molecular materials with a view to imparting functionalities to the materials. For instance, copolymers of styrene and divinylbenzene having sulfo groups introduced by means of sulfuric acid, chlorosulfonic acid, etc. have been used as cation exchange resins of strong acid type, and polystyrenes sulfonated by a similar method have been used as surface active agents. It has also been known to produce fibrous adsorbents by forming side chains, such as styrene, on a base material, such as polypropylene fiber, by radiation graft copolymerization and sulfonation of the resulting side chains.
It has been reported that among the above-described flame resistant fibers, those of polyacrylonitrile origin contain carbonyl groups of acridone type, and that active carbon fibers of high hydrogen sulfide adsorptivities can be obtained by activating them at 800.degree.-1,000.degree. C. However, the fibers do not have functionalities, such as absorptivity and ion exchange ability, when they have only undergone a flame resisting treatment of oxidation at 250.degree.-300.degree. C. Sulfonated products of styrene-divinylbenzene copolymers are insoluble in water but are partially soluble in organic solvents such as quinoline and DMSO. Sulfonate polystyrenes are also soluble in water. Moreover, these sulfonated polymers have low heat resistances of 100.degree. C. or below as well as low strengths. Further, in the case of radiation graft copolymers, their preparation has to be done by a particular process using radiation and, in addition, the heat resistance of the resulting fibers is no more than that of the substrate fibers.